1. Field of the Invention
This invention relates to an apparatus for and a method of filtering suspension to separately recover filtrate and concentrated suspension, and more particularly to a filtration concentration apparatus and method which are improved in efficiency in removing filter cake accumulated on a filter material to assure a high filtration operation efficiency.
2. Description of the Prior Art
A vertical filter is known as an apparatus for filtering and concentrating a large amount of suspension. The vertical filter includes a tubular filter material in an original liquid chamber at a lower location and has a filtrate chamber provided at an upper location and communicated with the inside of the tubular filter material. In order to filter and concentrate original liquid using the filter, the original liquid is pressurized by a pump or a like element and supplied into the original liquid chamber while filtrate is recovered from the filtrate chamber. When filter cake is accumulated around the filter material and consequently the filtration efficiency is deteriorated, supply of the original liquid is stopped first, and then a waste liquid pipe connected to a lower portion of the original liquid chamber is opened to discharge the original liquid while pressurized air is simultaneously supplied, if necessary, into the filtrate chamber to cause the filtrate in the filtrate chamber to flow reversely to backwash the filter material. Thus, liquid containing filter cake exfoliated from the filter material is sent by way of the waste liquid pipe to a waste liquid tank provided separately to restore the filtration efficiency.
With the filtration concentration method described above, however, since the filtration operation is stopped and a washing reconditioning operation of the filter material is performed when filter cake is accumulated on the filter material, when it is tried to process original liquid having a high suspended substance concentration, the filtering step must be interrupted frequently. Consequently, not only the time required for the backwashing step but also the time required for change-over between the steps is increased as much, and accordingly, there is a problem in that the operation efficiency of the filter is deteriorated.
On the other hand, a countermeasure to increase the pressure of air to be supplied into the filtrate chamber to raise the reverse flow rate of the filtrate is conventionally employed in order to reduce the time required for the filter material backwashing step. However, the countermeasure is disadvantageous in that it has an economical restriction since the apparatus must have a high pressure resisting property when the pressure in the filtrate chamber is high and besides that there is a limitation in reduction of time and the filter material is liable to be damaged.